The antigravity upstream-passthrough path (account.Type == AccountTypeUpstream
forwarding to a Claude-format upstream) drains the SSE stream via
streamUpstreamResponse + extractSSEUsage. The extractor only reads top-level
event["usage"], which matches Anthropic's message_delta but misses
message_start where usage is nested under event.message.usage.
As a result, every streaming /v1/messages request through this path drops
the input-side fields (input_tokens, cache_read_input_tokens, cache_creation_*)
and writes a usage_logs row with input_tokens=0 + output_tokens>0. The user
in #2332 observed 2,728 such rows attributed to claude-opus-4-6 / haiku-4-5
streaming requests; their billing on output is correct but the input-side
accounting is missing. (Their "duplicate write from message_delta" hypothesis
isn't borne out by the code — RecordUsage is invoked once per request and
writeUsageLogBestEffort dedupes by request_id; what they're seeing is
single records produced by this buggy extractor.)
Branch on event.type so message_start reads from event.message.usage and
other events keep using event.usage, matching how parseSSEUsagePassthrough
already handles both shapes for the Anthropic OAuth / API-key / Bedrock paths.
Adds two extractSSEUsage table cases plus a TestExtractSSEUsage_StreamingSequence
that drives the message_start → message_delta sequence end-to-end; both fail
on main and pass with this change.
Fixes#2332
Co-authored-by: Cursor <cursoragent@cursor.com>
1e6d0b602a